We have a LG GN-422FW. It starts OK, the temperatures in both compartments drop rapidly and stay down for about 1 hour, then the temperatures start to go upwards, more so in the Fridge than the Freezer. After a few hours the Fridge temperatures are cycling above the safe range for food storage.

It seems that the compressor is OK, however I suspect something else in the circuit is affecting the proper operation of the unit.

The fans all work. The fan in the back seems to work in conjunction with the compressor.

The fan & compressor is off while the temperature rises well above where it should be, again something is not turning the system on when it should be on.

The freezer thermister controls the temp in the freezer side. Depending on the resistance level, it tells the board to out put voltage to the compressor and fan circuit to bring the temp back to the thermister level. If the thermister is not doing its thing, the board will not fire up the compressor/fan. If the fridge side is the problem, there is a thermister in the damper housing, that controls the damper open and closing. I usually make sure the thermisters are not the issue before changing the boad.